1. Field of the Invention
This invention relates to porosimetry which is the measurement of the porosity characteristics of materials. More particularly, it relates to porosimeters of the mercury intrusion type.
2. Description of the Prior Art
In mercury intrusion porosimeters, mercury which is a non-wetting cohesive liquid, is forced into the pores of a sample of a charge of a material whose porosity is to be determined and the volume of the amount of mercury caused, in this manner, to permeate the sample charge and the pressure at which it is so caused, is measured. The results of such measurement can then be used to determine porosity characteristics of the material, such characteristics being, for example, pore volume, pore size distribution, surface area, absolute particle density and complexity or pores.
In the patent application of Krishna M. Gupta for Porosimeter, Ser. No. 917,347, filed June 20, 1978, and now U.S. Pat. No. 4,203,317, there is disclosed an efficacious porosimeter of the mercury intrusion type. The disclosure of patent application, Ser. No. 917,347, is hereby incorporated by reference into this patent application.
The porosimeter disclosed in patent application Ser. No. 917,347, essentially comprises a sample chamber, a tube disposed over the chamber and communicating therewith, a differential transformer type transducer disposed around the tube, a mercury source, and means for evacuating and thereafter introducing pressure into the arrangement. This porosimeter structure consists of components which are rugged, being made of a material such as stainless steel, and are constructed such that they can be placed in pressure tight relationship.
In the operation of this porosimeter, a weighed sample charge of a material whose porosity characteristics are to be determined is first placed into the sample chamber. The structure are then all made pressure-tight and the system is evacuated to as near a vacuum as is possible. Mercury is now permitted to flow to fill the sample chamber and air is then carefully introduced into the system to force mercury into the tube to fill it with mercury to a desired operating height. The tube contains a ferromagnetic body which has a specific gravity such that it floats in the mercury, and is suitably of a right circular cylindrical configuration, this body operating as the movable core of the differential transformer. After the tube has been filled with mercury to a position where the core is positioned to give a desired initial pre-reading on a voltmeter connected to the transformer, pressure is applied to the mercury in the tube and the chamber by the introduction of further air pressure into the system, and, if required, by added pressure generating means to cause the mercury to as completely as possible intrude into and permeate the sample. As a result of such pressure application, the height of the mercury in the tube is caused to drop. The resulting new height of the mercury is sensed by the transducer and recorded on the voltmeter. In this manner, the volume of the mercury intruded into the sample is obtained. The value of this volume and the value of the pressure applied, enable the determination of the various porosity characteristics of the sample as has been mentioned hereinabove.
As has been stated, the porosimeter disclosed in patent application, Ser. No. 917,347, is generally quite effective for the purposes to which it is put. However, the results obtained with it when the porosity characteristics of a material having relatively large pores is being determined are not as precise as in the case where the material has smaller pores. To understand the reason for this imprecision, it is to be realized that the larger the pores, the less resistance there is to the intrusion thereinto of mercury. Therefore, whereas a small pore material may require great amounts of pressure to force mercury therethroughout, comparatively little pressure may be required to permeate with mercury a material having relatively large pores.
Thus, in the operation of this porosimeter, when air pressure is first introduced into the evacuated system to force the mercury into the tube, this small amount of pressure on the mercury has a negligible effect on the precision of the finally attained mercury volume in the case where a small pore material is being examined, since little if any mercury will be forced into its pores. However, where the material has relatively large pores, this small amount of pressure that has to be introduced to force the mercury into the tube can cause a large enough amount of mercury to enter the material sample so as to render the final results less precise than desired. Ideally, any imprecision so introduced can be eliminated if such pressure is used only to cause mercury to intrude into the sample and no portion thereof has to be initially used to fill the tube.
Accordingly, it is an important object of this invention to provide a porosimeter arrangement of the type disclosed in patent application, Ser. No. 917,347, wherein the porosity characteristics of materials can be precisely determined irrespective of the size of the pores.
It is another object to provide a porosimeter arrangement in accordance with the preceding object wherein pressure is employed essentially only to cause mercury to intrude into the sample of the material whose porosity characteristics are being determined.
It is a further object to provide a porosimeter assembly in accordance with the preceding objects wherein there is enabled the concurrent porosity determination of a plurality of samples.